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This paper presents results of a study on the feasibility and performance impact of using water injection on a Boeing 747-400 aircraft to reduce NOx emissions during takeoff. For the primary PW4062 engine studied, injecting water directly into the combustor was the preferred method. Using a 1:1 water-to-fuel injection ratio is estimated to yield an 80% NOx reduction along with a potential reduction in smoke during takeoff. This would require 400 gal of conditioned water to be used onboard the aircraft during takeoff to 3000 ft (914 m) altitude. The engine's turbine inlet temperature would be reduced by over 120 GradF (67 K). Engine operation at reduced temperatures also holds the potential for hot section life improvement. Up to a 29% increase in turbine life may be expected. Performance penalties include an approximately 750 lb (340 kg) increase in aircraft weight that could reduce range by 60 n mi. Another challenge of water injection is its increased propensity to cause the compressor to stall, or reduce the stall margin. The resulting high development costs, coupled with engine performance penalties on older designs, will make the system unattractive as a retrofit option. However, for a newly designed engine and airframe, some of these costs and penalties may be reduced. If one considers the full potential for the longer lived turbine's positive impact on engine maintenance costs, the system was estimated to have potential savings for an operator of a newly designed airplane of up to 1.0% in operating costs.